
// 借助symobol
let x = Symbol()
class A {
    constructor(a) {
        this[x] = a
    }

    getA() {
        return this[x];
    }
}



// 借助闭包
(() => {
    let x = {}
    class A {
        constructor(a) {
            this[x] = a
        }
        getA() {
            return this[x];
        }
    }
    return A
})()